-LRB- CNN -RRB- -- Michigan Gov. Rick Snyder 's stunning decision to sign a right-to-work law poses the question : Are these anti-union statutes , which make illegal any union contract that requires union membership or payment of dues a condition of employment , the future ? During the last two years Indiana and Wisconsin have also passed laws that curb union strength and slash dues income .

`` If Michigan can do it , then I think everybody ought to think about it , '' asserts Mark Mix , president of the National Right to Work Legal Defense Foundation . Mix listed Alaska , Missouri , Montana and Pennsylvania , where Republicans enjoy large majorities in state legislatures , among the top contenders .

The potential spread of right-to-work laws in the North , even in states where voters heavily favored President Obama for a second term , is a startling and ominous development .

For decades , right-to-work laws were confined to the South or Mountain West , heavily agricultural states where new unions born during the Depression era evoked , among many employers and conservative politicians , the specter of Communism , race-mixing or both . These laws were almost all enacted in the years after the 1947 Congressional passage of the Taft-Hartley Act , which gave states the right to make illegal any collective bargaining contract that mandated union membership as a condition of employment .

Opponents of unionism hailed these laws as insuring a `` right-to-work '' because they encouraged workers to take a job , even one where the wages and working conditions had been negotiated by a union , without paying the dues necessary to sustain the labor organization . To note that employers encouraged such free-loading would be an understatement . Then and now they denounced `` compulsory unionism '' and the `` labor bosses '' who sought to live high on the hog on member dues . In this imagining , it was the union , not the employer , who oppressed the workers .

Opinion : A victory for right-to-work laws

In 1958 , right-to-work advocates thought the time was ripe to invade the North . A sharp recession in the late 1950s had sapped union strength at the same moment that the Senate 's McClellan Labor Rackets Committee investigation had uncovered unsavory links between Jimmy Hoffa , the Teamsters , and organized crime . Urged on by conservative Republican Sen. Barry Goldwater and financed by a newly created National Right to Work Committee , these anti-union activists put right to work referenda on the ballots of California , Ohio , Washington , Kansas , Idaho and Colorado .

But with the exception of Kansas , all these initiatives went down in overwhelming defeat . That was not only because labor was still a powerful force -- in Ohio union density , the proportion of all workers in a union , stood at nearly 40 % -- but also because the Democrats linked their fortunes to the labor movement and to the fight against right to work . As Pat Brown , the California gubernatorial candidate put it , right to work represented `` a return to the ugly and destructive law of the economic jungle . ''

The battle for the votes of African-Americans constituted one of the most remarkable features of these referenda . Right-to-work advocates pointed out , often quite accurately , that many American trade unions failed to adequately represent their minority members . If unions were weaker , minority workers might well get better jobs and promotions . But in Ohio and California especially that argument failed to persuade .

The NAACP distributed a pamphlet entitled `` Keep Mississippi Out of California , '' but even without this kind of propaganda most African-Americans and Latinos knew that an imperfect union was a better friend that a non-union employer whose power and prejudices ruled the workplace unchecked by any countervailing institution .

Today , right-to-work forces are once again making a push to eviscerate unionism in its heartland . Thanks to Citizens United they have unlimited money . Thanks to globalization , slow growth , and corporate attacks , trade unionism is far weaker than in 1958 .

In Ohio union density stands at 13.4 % , in Pennsylvania 14.6 % , in Michigan , birth state of the once powerful United Automobile Workers , just 17.5 % , a disastrous drop since the industrial union heyday in the 1950s .

To staunch this anti-union assault , the Democrats have to make the defense of union rights and power a central , organic component of their message to American voters , office holders and workers -- both white collar and blue . Although Democratic legislators in Wisconsin , Michigan and Ohio have bravely fought the Republican right on this issue , President Obama has been notably missing from the action .

Obama denounced `` right to work for less '' in a post-election speech at a factory outside Detroit , but he was almost entirely silent on the issue both during the demonstrations that convulsed Madison , Wisconsin , in the winter of 2011 , during the effort to recall Wisconsin Gov. Scott Walker in the spring of the next year , and throughout the presidential campaign itself .

Obama and his advisers undoubtedly thought that if they wanted to win right-to-work states like Virginia and Florida , they better keep quite about union rights in the North . But this was and is an exceedingly shortsighted and self defeating calculation .

Trade unions stand at the core of the Democratic coalition . They are the last organizations remaining on the liberal side that can effectively appeal to white , working-class men in the Rust Belt swing states . Without the union organization and mobilization of blue collar Latinos in California , Nevada , and New Mexico those states would be almost as red as Texas .

When Obama declared his support for gay marriage , he helped consolidate a growing national consensus in favor of that right . The president and other national Democrats need to use the same bully pulpit to defend trade unionism in its hour of need , not only because their destruction threatens the living standards of our working middle class , but because these institutions are the living embodiment of democracy , interracial solidarity and personal dignity in the world of work .

The opinions expressed in this commentary are solely those of Nelson Lichtenstein .

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Nelson Lichtenstein : Will more states pass right-to-work laws like Michigan ?

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Lichtenstein : The potential spread of the laws in the North is startling and ominous

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He says opponents try to paint the union , not the employer , as oppressors of workers

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Lichtenstein : President Obama need to defend trade unionism in its hour of need